Abrasive grits or particles have long been employed in abrasive products. These abrasive products include bonded abrasives (e.g. grinding wheels), coated abrasives, and nonwoven abrasives. Preferred abrasive grit is typically tough, hard, and chemically resistant to the workpiece being abraded. A "tough" abrasive grit is generally strong and fracture resistant. A "hard" abrasive grit generally resists yielding or dulling from the forces of grinding. When the abrasive grit does yield or dull, this typically leads to decreased abrading performance.
One common type of aggressive abrasive grit, known as fused alumina, is formed by heating a source of aluminum oxide to a molten state, rapidly cooling and then crushing. This type of abrasive grit is hard, tough, and chemically resistant.
A more recently developed type of abrasive grit is often referred to as alpha alumina-based ceramic abrasive grit. This type of abrasive grit can be made by a sol-gel process, wherein, for example, a dispersion comprising a liquid medium (typically water), alpha alumina monohydrate, and optional additives such as metal oxide precursors (e.g., magnesium nitrate), is dried, crushed, calcined, and then sintered. The resultant ceramic abrasive grit is typically tougher than the fused alumina grit, and typically exhibits superior performance in abrading operations.
Abrasive products containing sol-gel based alpha alumina grits or particles have been in commercial use for up to 15 years. During this time, there have been numerous improvements made to the alumina abrasive grits or particles. Some of these improvements concern modifications to the crystal structure (referred to as the microstructure) of the alpha alumina crystals which form the abrasive grits or particles. The abrasives industry has, in general, been seeking higher performing alumina abrasive particles to incorporate into abrasive articles.